I probably should have posted this here first. I tried this on DGCR and despite my request to limit verbose replies steeped in conjecture and ill-informed nonsense, that's exactly what I got. I know that these topics have all been covered on DGR before, but I need to get this info all in one place so I can respond to a question a buddy asked me. Specifically, I'd like to know how the weather variables below impact the flight of a disc from the following standpoints: More/Less Distance, More Overstable/More Understable, More/Less Glide. Assuming all other variables are at some national and seasonally-adjusted average and held constant, can someone fill in the following details to indicate how changes to each of the following environmental variables would impact disc flight?

bcr123psu wrote:I probably should have posted this here first. I tried this on DGCR and despite my request to limit verbose replies steeped in conjecture and ill-informed nonsense, that's exactly what I got.

I'm still being amused by the discs speeding up after they leave the hand.

Higher air density means the disc will slow down faster, but the cruising speed window is lower as well, meaning the disc will begin to turn at a lower speed threshold, and will begin to fade at a lower speed threshold as well. Discs will also move more left or right based on the same relative hyzer/anhyzer angle than in lower air density (think about trying to turn on ice vs asphalt; higher density = more "traction" due to air resistance (yes I know "traction isn't the correct term, but it gets the point across)).

Lower air density would be the opposite. The disc will maintain speed better (meaning out of the hand speed is the same). The cruising speed window is overall higher. Discs require more speed to turn and fade at a relatively higher speed as well. Discs will also not move quite as much left or right based on hyzer or anhyzer angle.

The reason I won't speculate on distance for either of these is both conditions have their pros and cons with regards to maximizing. I would assume you could manipulate variables to account for differences and have the same distance potential. Don't quote me on that though.

bcr123psu wrote:I probably should have posted this here first. I tried this on DGCR and despite my request to limit verbose replies steeped in conjecture and ill-informed nonsense, that's exactly what I got.

I'm still being amused by the discs speeding up after they leave the hand.

My logical thinking would tell me that LOWER humidity means lower air density. When you have lower humidity, you have less molecules in the same space like you have when its more humid...right? Or did my brain mess anything up...?

But as kern already explained, distance +/- isn't necessarily correct, it always depends on how you throw. Like he already said, higher air density means that there are more molecules in the air that can carry the disc but will also result in more drag on the disc.

I can imagine altitude and temp have an effect when the Δ is dramatic (can't tell you any numbers, maybe the more experienced players can though), but humidity...not that sure

Luma, it's counter intuitive but he is correct. water vapors are actually lighter than dry air molecules. Hydrogen is much lighter than everything else in air. So say a dry air is composed 80% Nitrogen and 20% Oxygen (Just a ballpark, there's many other chemicals involved.) once you start increasing the humidity, it's going to need to replace those other heavier molecules with a much lighter Hydrogen. Avogadro's Law explains that you can't just add to this dry air mixture, the hydrogen actually has to replace something and I'm simplifying it pretty hardcore.

Basically, if I have 100 "dry air molecules" compiled of 80% nitrogen(14amu), 20% Oxygen(16amu)=~1460amu. versus 100 "humid air molecules" that are composed of 79% nitrogen, 19% oxygen and 2% hydrogen(1amu)=~1432amu.

Most people are used to dealing with gases mixing in a closed environment with a fixed volume. In this case, you can add water vapor (increase humidity), and to compensate for the added mass, you increase pressure, since volume is fixed.

The reason humidity making air less dense seems counter intuitive is that we are looking at the same gaseous pressure problem in a completely different manner. If you look at a system with a fixed pressure, and add water vapor, you are increasing volume, therefore adding less dense molecules (water vapor) to more dense molecules (dry air) will cause a decrease in density.

The best example I can give to help visualize this is a balloon. A balloon forms a closed system where, conditions being impossibly ideal, the air pressure inside the balloon and outside the balloon are at equilibrium, because the balloon can change volume to compensate for this. If you increase pressure outside the balloon, without changing the mass of the gas inside, the balloon will shrink, so as to equalize the pressures pushing in from the outside and out from the inside of the balloon.

Because of this, you can say that a balloon is a system with a (relatively) fixed pressure.

For dealing with fixed pressure, we can do this. (I'm throwing the ideal gas law out there, google it if you want to know more about it)

PV=nRT

P= PressureV= Volumen=moles of gas; for those non-chemists/physicists, this is a way of counting the actual number of molecules in a sample regardless of massR=a constantT= Temperature

We'll have 3 constants in this equation; pressure, temperature, and R, so we can rewrite the equation like this:

P/(RT) = n/V = n(1)/V(1) = n(2)/V(2)

The last two part of that equation will be the parts we'll focus on. IF we start with 1 mole of gas in 1 L, and add another mole of gas, the volume of the system will double to 2 L. It would look like this:

1 mole/1 Liter = 2 moles/2 Liters

Hopefully this is seeming more intuitive looking at it this way. What you should be taking from this is that adding gas increases volume. Self explanatory. More importantly, the volume of the gas increases with absolutely no relation to the mass of the gas. If you are adding a lightweight gas (water vapor in this case) you are increasing the volume more significantly than you are increasing the mass. Density is mass/volume if you recall. Anytime you are increasing volume more, you are lowering density.

Probably WAY more of an explanation than anybody was looking for, but there it is in a nutshell (sorta).

The unfortunate truth is that terms such as "stable" and "glide" are meaningless. Next time somebody tells you a disc has a stability (or glide) of 3 (for example) just ask them: 3 what? What are the units, what exactly is this measuring, and how can you reproduce their measurement? And while "distance" can be measured, it is known to be a complex mixture of many factors. Ratings using Speed/Glide/Turn/Fade are pretty stupid, and a lot of important real physics are glossed over in the process of using it. Discs are so much more than just 4 meaningless numbers, and everybody who has thrown a lot knows that such a primitive rating doesn't cover a lot of variety that occurs in real discs.

As others mentioned, altitude, heat, and humidity all decrease the density of air. Meteorology has constructed very accurate equations for the effects of all these things, you can find some calculators posted on some websites if you google.

Provided that the change in density doesn't change the planform of air flow around a disc appreciably, then for a disc flying at a given air speed and angle of attack, a lower air density results in relatively:1) smaller lift force (but what matters is relative to weight of the disc, this can be compensated by lighter plastic)2) smaller drag force (flies "faster")3) smaller torques (turns over less, fades less)

Think about taking it to the limiting extreme of disc "flying" in a vacuum (outer space), which has no lift, no drag, and no torque...by lowering density, this is the direction you're going.

To compensate for low air density, use lighter plastic and bring some under-stable discs that will turn over more easily. And bring older slower discs, too...I was always amazed at how far I could throw a Comet at the Tahoe courses (they're going to bid for 2015 Worlds).

JHern wrote:The unfortunate truth is that terms such as "stable" and "glide" are meaningless. Next time somebody tells you a disc has a stability (or glide) of 3 (for example) just ask them: 3 what? What are the units, what exactly is this measuring, and how can you reproduce their measurement?

Right, but there's no denying that the few discs rated at 6 glide like crazy compared to the 3s, no matter what is actually being measured. I find it valuable even if not ideal.

Ouch, I'm really ashamed but actually I'm at university studying material sciences, and last half year I've had thermodynamics there, but our prof. was kind of an idiot so I've never been there.... but I knew that pV=nRT stuff for the exam And now that you explained...well, sometimes my brain takes it way to easy.

To compensate for low air density, use lighter plastic and bring some under-stable discs that will turn over more easily. And bring older slower discs, too...I was always amazed at how far I could throw a Comet at the Tahoe courses (they're going to bid for 2015 Worlds).

If Tahoe is high altitude then I pray they don't get Worlds.

No offense to Tahoe (or any high altitude location). I played Denver a few years back and none of my discs flew even close to normally. I don't need to learn a bunch of new courses AND re-learn to throw every disc in my bag.